1. Field of the Invention
The present invention relates to the use of a secondary amine as a corrosion inhibiting and antimicrobial agent especially cially in an aqueous alkaline industrial fluid, such as an aqueous metal working fluid. The effects of the secondary amine are especially favourable at a pH value above 8.
2. Description of the Related Art
Water-based alkaline industrial fluids, such as metal working fluids, hydraulic fluids, coolants and cleaning fluids, undergo after some time of use or storage undesirable changes which can be related to the fact that the components included in the fluids are degraded by bacteria, fungi and other micro-organisms. The microbial degradation considerably reduces the life and the performance of the fluids. For example the microbial degradation of the fluids may destroy the corrosion inhibiting and lubricating properties. From an economic point of view, it is therefore of great importance that microbial degradation of fluids of this type be minimised.
Well-known antimicrobial agents used in metal working fluids are formaldehyde or compounds giving off formaldehyde. Since formaldehyde readily evaporates from the fluid in open systems, the formaldehyde content will be successively reduced and the surrounding air contaminated with formaldehyde at the same time.
Other antimicrobial agents are quaternary ammonium compounds, but their use, e.g. in metal working fluids, has involved many practical problems, for instance because of reaction with organic acids and anionic surfactants that may be present in the formulation.
The use, as antimicrobial agents, of reaction products of boric acid and a number of organic compounds, such as alkanolamines and carboxylic acids is also known in cutting fluids. However, such reaction products have been found to have a relatively low antimicrobial effect, primarily on fungi, and must therefore be used in relatively large amounts.
From articles by E. O. Bennett, e.g. his article in J. A. Soc. Lubr. Eng., 35 (1979), 137-144, U.S. Pat. No. 4,749,503, and European Patent Application 412 089, it is known that secondary and tertiary alkanolamine compounds substituted by hydrocarbon groups having 1-18 carbon atoms have an antimicrobial effect in cutting fluids and coolants.
The use of a number of alkoxylated amines and alkanolamines in order to obtain a tool life extension is known from European Patent Applications Nos. 196,810 and 192,358. For metal working fluids containing N-methylethanolamine a lowered susceptibility to the growth of mold and bacteria is reported. From the European Patent 180,561 it is also known that certain tertiary alkanolamines have corrosion inhibiting effects in metal working fluids.
Alkanolamines, such as monoethanolamine, diethanolamine, diisopropanolamine and triethanolamine, have frequently been used as corrosion inhibiting agents in aqueous alkaline industrial fluids. From U.S. Pat. Nos. 3,280,029 and 4,976,919 and European Publication No 180,561, it is well-known to use secondary and tertiary alkyl alkanolamines as corrosion inhibiting agents.